1. Field of the Invention
The invention relates to an apparatus and a module, and more particularly to a digital sensing apparatus and a digital readout module with an adjustable readout range.
2. Description of the Related Art
FIG. 1 shows a conventional sensing apparatus SA including a sensing element SE, a reading unit RU′, and an analog-to-digital converter ADC.
The sensing element SE is configured to sense an environmental parameter and to generate a first characteristic parameter varying in a positive relation with the environmental parameter, and a second characteristic parameter varying in a negative relation with the environmental parameter.
The reading unit RU′ is electrically coupled to the sensing element SE for receiving the first and second characteristic parameters, and generates a sensing voltage that varies in a positive relation with a difference between the first and second characteristic parameters.
The analog-to-digital converter ADC is electrically coupled to the reading unit RU′ for receiving the sensing voltage therefrom, and is operable to perform an analog-to-digital conversion on the sensing voltage falling within a conversion range, so as to generate a digital sensing code associated with the environmental parameter.
In order to efficiently use all the bits of the analog-to-digital converter ADC, the upper and lower limits of the conversion range of the analog-to-digital converter ADC must correspond to the upper and lower limits of the sensing voltage produced by the reading unit RU′, while the upper and lower limits of the sensing voltage correspond to a readout range of the sensing apparatus SA. If the environmental parameter sensed by the sensing apparatus SA is outside of the readout range, the digital sensing code generated by the sensing apparatus SA may have an error.
For illustration, the conventional sensing apparatus SA may be exemplified using an accelerometer. The conversion range of the analog-to-digital converter ADC ranges from 0V to 5V and is represented using 10 bits.
Referring to FIG. 2, the sensing element SE includes a central mass CM that is capable of producing a displacement associated with an applied acceleration, and left and right masses LM, RM that are immovable with respect to the environmental parameter and disposed at two opposite sides of the central mass CM. The masses LM, CM, and RM are electrical conductors, so as to form an equivalent left capacitor CL between the central mass CM and the left mass LM, and an equivalent right capacitor CR between the central mass CM and the right mass RM.
When acceleration is applied to the sensing element SE in the right direction, the central mass CM will move towards right, and the displacement value of the central mass CM during a unit time period is in a positive relation with magnitude of the acceleration applied thereto, such that the central mass CM becomes closer to the right mass RM and farther from the left mass LM, resulting in larger capacitance CR of the equivalent right capacitor CR (which is the first characteristic parameter) and smaller capacitance CL of the equivalent left capacitor CL (which is the second characteristic parameter).
The reading unit RU′ is a capacitance-to-voltage converter that is capable of producing the sensing voltage varying in a positive relation with a difference ΔC between the capacitances CL, CR of the equivalent left and right capacitors CL and CR (ΔC=CL−CR or ΔC=CR−CL).
The analog-to-digital converter ADC is electrically coupled to the reading unit RU′ for receiving the sensing voltage, and is operable to perform the analog-to-digital conversion on the sensing voltage falling within the conversion range (0˜5V in this example), so as to generate the digital sensing code associated with the environmental parameter. When the sensed environmental parameter is equal to the lower limit of the readout range (for example: −2 g), the sensing voltage is 0V, and the digital sensing code is (0V/5V)×1023=0. When the sensed environmental parameter is equal to the upper limit of the readout range (for example: +2 g), the sensing voltage is 5V, and the digital sensing code is (5V/5V)×1023=1023.
However, when the sensed environmental parameter is +3 g, the sensing voltage obtained from the above calculation should be 6.25V, which exceeds the upper limit 5V of the conversion range, and the digital sensing code is not able to correctly correspond to the environmental parameter +3 g.
Therefore, the aforesaid conventional sensing apparatus has the following drawbacks:
1. The readout range is fixed, and the digital sensing code which ranges between 0 to 2N−1 from the N-bit analog-to-digital converter ADC corresponds to the readout range between the lower and upper limits. When the sensed environmental parameter exceeds the readout range, the generated digital sensing code may have errors.
2. The analog-to-digital converter ADC must perform conversion continuously, resulting in large power dissipation.